Color photographic materials which are now generally distributed in the market are composed of silver halides as light-sensitive elements and color couplers as color-forming elements. When such a color photographic material is imagewise exposed and then processed with a developer containing an aromatic primary amine compound as a developing agent, only the exposed silver halide grains in the material are reduced to a metal silver by the developing agent. The oxidation product of the developing agent to be formed by the reduction is coupled with the couplers in the material by a coupling reaction to form dyes. As a result, a color image which corresponds to the exposed pattern is formed in the material. The metal silver formed by development and the non-developed silver halides are removed by the successive bleaching and fixation steps to yield a stable color image. When yellow-coloring, magenta-coloring and cyan-coloring couplers are incorporated into the photographic material, reproduction of a natural color image is possible by the subtraction process of the three primary colors.
The color image-forming system based on the principle is the most popular one in the current technical field, and various studies on the system are being made for the purpose of improving it.
The most important approach to improving the color image-forming system is to shorten the access time. For instance, in the market of color prints, there is an increasing demand for finishing a large number of color prints in a short period of time. Because of that demand, rapid processing of photographic materials in a shortened period of time is an important goal. In order to achieve the goal, therefore, many reports have been made relating to silver halide emulsions having a high development rate, couplers having a high coupling activity and processing agents capable of rapid development. As an example, International Patent Application Laid-Open No. WO87-04534 illustrates a method of processing a color photographic material having a high silver chloride emulsion with a color developer containing substantially no sulfite ion or benzyl alcohol.
However, when a printing color photographic material having a silver halide emulsion with an elevated silver chloride content is used to form a color print, it has been found to yield poor results at the point of color reproduction. Precisely, when a color print is formed from a negative film which is exposed to take a picture from an object having a high chroma (for instance, red flowers or wears), using a photographic material of that type, satisfactory reproduction of the shadow-tone of the object is impossible. Only an image which lacks a three-dimensional and solid sense is obtained.
As a result of the inventors'analysis of this problem, it has been determined that the problem is caused by the difference in intrinsic sensitivity distribution between the silver chlorobromide emulsion which has heretofore been used in conventional printing color photographic materials and the high silver chloride emulsion which has been developed for rapid-processable color photographic materials.
In general, a silver halide emulsion constituting the light-sensitive element of a color photographic material has (i) a so-called intrinsic sensitivity, which is the sensitivity corresponding to the light-absorption of the silver halide itself, and (ii) a so-called color-sensitivity of blue-sensitivity, green-sensitivity or red-sensitivity, which is imparted to the emulsion for reproduction of a natural color. The longest wavelength of the distribution of the intrinsic sensitivity, depends upon the halogen formulation of the emulsion grain. For instance, a pure silver chloride emulsion has a wavelength of about 400 nm, a pure silver bromide emulsion has a wavelength of about 500 nm, and a mixed silver halide emulsion of them has a value which is proportional to the halogen formulation. Accordingly, a printing color photographic material having a silver chlorobromide emulsion has a sensitivity, as the total light-sensitive layer, to a blue light having a high strength, while another material having a high silver chloride emulsion does not have a sensitivity to blue light. Consequently, employment of such a high silver chloride emulsion is extremely advantageous for reproduction of high-purity yellow and green. On the contrary, however, expression of shadow of an object having a high chroma is impossible with a high silver chloride emulsion. As a result, a high silver chloride emulsion yields only a flat image, but not solid or cubic one. When a silver chlorobromide emulsion is used, expression of the shadow of an object having a high chroma is possible, but the yellow and green colors of the reproduced image are not clear. (For instance, a cyan color gradation is expressed in a dark red image.)
Some techniques for overcoming this drawback of high silver chloride emulsions have been proposed. For instance, U.S. Pat. No. 4,806,460 illustrates a photographic material which may yield an additional cyan gradation when the image density of yellow or magenta exceeds a predetermined density. European Patent 304,297A2 illustrates a technique of adding a green-sensitizing dye to a red-sensitive emulsion layer containing a cyan color-forming coupler.
However, it has been found that the photographic materials prepared by these proposed techniques have various drawbacks. First, in order to attain faithful tone reproduction without making a pure color turbid, the gradation to the second color sensitization (blue-sensitization or green-sensitization) to be applied to the silver halide emulsion in the cyan-coloring layer must be controlled exactly. However, the gradation in the blue-sensitive area or the green-sensitive area often becomes soft because of the difference in the sensitizing characteristic between the red-sensitizing dye and the blue-sensitizing or green-sensitizing dye. Second, the sensitivity and gradation of the red-sensitive area and those of the blue-sensitive or green-sensitive area often vary and fluctuate during the course of preparation of photographic materials or during storage of the coating compositions before coating. This variation or fluctuation also occurs during storage of the prepared photographic materials. In other words, the stability of the photographic property of the photographic materials prepared by these prior art techniques is poor.
Thus, improvement of the stability of the tone reproducibility in photographic material having a rapid processable high silver chloride emulsion is an extremely important matter for the purpose of satisfying both goals of a high producibility of the material and an excellent image quality of the image formed on the material.